This invention relates to the continuous casting of molten metal, e.g. aluminum and its alloys, into ingots of indeterminate length. More specifically, this invention relates to methods of making molds for continuous casting of molten metals and to the construction of such molds.
Continuous casting of molten metals into ingots of any desired length is well-known and many molds to permit continuous casting of, for example, aluminum and aluminum alloys have been described in the art.
Wagstaff, et. al., in U.S. Pat. No. 3,688,834, Sep. 5, 1972, describe one mold construction for continuous casting of molten metals, this patent being directed to the inherent problem of thermal warpage of the mold arising from temperature differentials. Since, portions of the mold are water cooled and portions of the mold are in contact with the molten metal thermal warpage is inherent in the structure.
Wagstaff, et. al. for over a quarter century have been designing and improving molds for continuous casting of molten metals. The above-mentioned patent and those referred to hereinafter are incorporated herein as representing the development of the art and the present state of the art. The following Wagstaff, et. al., U.S. patents are incorporated by reference: U.S. Pat. No. 3,739,837, Jun. 19, 1973, (cooling chamber construction); U.S. Pat. No. 4,598,763, Jun. 8, 1986 (directly cooled, unitary annular graphite casting ring); U.S. Pat. No. 4,693,298, Sep. 15, 1987, (controlling direct cooling rate of graphite in continuous casting of molten metal); U.S. Pat. No. 4,947,925 (direct cooling of graphite casting ring made up of clamped graphite components); U.S. Pat. No. 5,191,924, Mar. 9, 1993 (built-up ingot mold having a large pair and a small pair of cooled plates with comer fittings); U.S. Pat. No. 5,318,098, Jun. 7, 1994 (graphite ring casting mold); U.S. Pat. No. 5,323,841, Jun. 28, 1994 (annular casting mold frame supported below, rather then above, a graphite casting mold made up of clamped components); and U.S. Pat. No. 5,518,063, May 21, 1996 and U.S. Pat. No. 5,685,359, Nov. 11, 1997) (continuous casting apparatus having graphite casting ring and use of liquid that cools the mold to directly cool the cast metal).
In addition, U.S. Pat. No. 5,678,623, Oct. 21, 1997, to Steen, et. al., which discloses a permeable unitary graphite casting ring, is incorporated herein by reference.
While the foregoing are considered to accurately represent the state of the art, there are many other patents and many publications that bear upon the subject.
The difficulties in making large graphite casting rings has been described and some solutions have been proposed, for example, in U.S. Pat. No. 4,947,925, which describes the graphite casting annulus made by clamping graphite side pieces and end pieces together. The term xe2x80x9cannulusxe2x80x9d is used herein generally in the same sense as that term is used in said U.S. Pat. No. 4,947,925, i.e. to mean an enclosed space, which may or may not be circular, surrounded by graphite. U.S. Pat. No. 5,323,841 discloses a similarly constructed annular casting annulus made up of clamped components.
Graphite casting annulus structures have, in the past, generally been round and generally been made of a unitary piece of graphite. The practice, still in wide use has many obvious advantages.
It is, however, difficult to make a large unitary casting annulus of a non-circular nature with machining, heating and forming equipment commonly available in the machine shop of a metal foundry or metal casting machine manufacturer.
Wagstaff, et. al., inter alia, proposed making a graphite casting annulus out of a plurality of graphite components, e.g., a pair of sides and a pair of ends. Since the entire graphite annulus must be liquid tight, i.e., there must be no space in the casting annulus into which the molten metal can flow, it is of the greatest importance that the graphite components be positioned closely in contact with each other. In the type of casting apparatus contemplated by Wagstaff, et. al., the graphite casting ring components are captured between upper and lower frame members to provide mechanical support and assure the positioning of the components. It was previously known to use the xe2x80x9cbarrel hoopxe2x80x9d concept of placing the components of the annulus in upper and lower frames and then clamping the components using a clamping band or other structurexe2x80x94as, in principle, has been the practice for centuries in the manufacture of steel banded wooden barrels.
This approach is not satisfactory in the manufacture of other than circular molten metal graphite casting structures because the clamping force is not uniformly applied and because graphite is quite brittle with virtually no resilience. Thus, Wagstaff, et. al., employed special clamping structures and methods in which the components were clamped before being positioned between the upper and lower frame members. Obviously, all of the graphite components must be in place and undamaged before any of them can be clamped. The Wagstaff, et. al, pre-clamping concept is an improvement that helps make the manufacture of larger sized graphite casting annulus molds; however, this concept also introduces complications in assembly, as referred to, and in repair wherein the entire annulus must be re-built to make a minor repair. Additionally, for rectangular ingot making, the size of the annulus can be very large, requiring intricate machining on a very large piece of graphite. Also, specific convex profiles have to be provided in the annulus wall contour and as such manufacture of the mold by the clamping method using large graphite pieces is highly time consuming and expensive from material and labor point of view.
The present invention permits the manufacture of large and varied shape graphite annulus casting molds from a multiplicity of graphite casting annulus insert components that are individually positionable and fixed individually in position without need for clamping.
The present invention is embodied in apparatus and methods for foundry operations that substantially reduce the raw material costs, machining time, annulus mold fabrication and assembly time, and thereby assembly costs, and mold maintenance and repair costs, leading to an overall substantial reduction in the cost of tooling and ultimately in the cost of foundering the metal.
The invention also provides a low cost alternative for building proto-type tooling required for forming ingots of different shapes and sizes, thereby increasing the flexibility of the foundry operation to quickly adapt to new and complicated sizes and cast product contours. The invention also provides a savings in tooling, spares, consumables and inventory costs.
The present invention may be described, in one facet, as an improved molten metal casting annulus that comprises, in combination, an insert support and cooling frame configured and constructed to define an enclosed planar annular space and defining an annular face that faces said annular space that is generally perpendicular to the plane of said annular space and a very large number multiplicity of graphite casting annulus insert components (where the number of graphite components would be more than 200 for 100 inches perimeter of metal casting annulus) supported entirely without clamping on said insert support and cooling frame. In a preferred form of the invention, the frame defines one or more annular grooves adjacent said annular face. The insert components are fitted edge to edge on the annular face to define a molten metal casting annulus. The insert components, in a preferred embodiment, defined a lip which is snugly fitted in an annular groove in the support and cooling frame for positioning and locking said insert components in therein.
In a preferred embodiment of the invention, the casting apparatus is designed to provide, in addition to the graphite annulus, a lubricating oil and an additional fluid medium selected from the group consisting of a highly heat vaporizable liquid medium with or without a gaseous medium that are simultaneously forced through the fluid permeable graphite components so that the oil and additional fluid medium discharge into the cavity at points on the inner peripheral surface of the casting face. Simultaneously, the molten metal body is chilled from points below the intermediate continuum.
In another preferred embodiment, the casting face of the insert components are coated with a slurry of sub-micron size colloidal graphite particles and molybdenum sulfide particles. These particles modify and define the characteristics of the casting face and provide a smooth stick resistant surface, over-coming any inconsistencies that may arise from the use of insert components not exactly the same thickness or which may have imperfections therein.
The lubricating oil with or without vaporizable liquids are preferably delivered by way of grooves on the back side, i.e., the side not facing the annulus, of the insert component are caused to diffuse simultaneously through the body of the ring, i.e., through each of the insert components, so as to discharge into the annulus at the inner peripheral surface of the casting ring while the molten metal mass is chilled and molded.
In certain embodiments, for example, the additional fluid medium is a gas. In the exemplary embodiment, the oil and gas are forced into the fluid permeable insert components through a plurality of spaced grooves extending about the rear of the graphite annulus , at the outer periphery thereof.
Fluid delivery means are also provided for simultaneously forcing a lubricating oil and an additional fluid medium selected from the group consisting of a highly heat vaporizable liquid medium with or without a gaseous medium, through the fluid permeable wall section so that the oil and additional fluid medium discharge into the cavity at points on the inner peripheral surface of the wall section opposite the intermediate continuum.
In a convenient embodiment, a lubricating oil is pumped into the aforesaid grooves along with a stream of pressurized gas such as air. Both oil and gas can be pumped into the same groove or grooves or, separately, into the respective groves so that the oil and gas diffuse simultaneously through the body of the graphite casting ring and discharge into the cavity at the inner peripheral surface of the casting ring while the molten metal mass is chilled to form the chilled mass into an elongated billet of the metal
The graphite is hot isostatically pressed or extruded, very fine grain, essentially flaw-free, high strength graphite such as the ATJ graphite sold by the Carbon Products Division of Union Carbide Corporation, Chicago, Ill. or equivalent grades provided by SGL Carbon Corporation of St. Marys, Pa. Preferably, it also machines to a fine surface finish and has a high thermal conductivity. Such graphite is sufficiently permeable to permit oil and gas to diffuse there through. In addition, such graphite permits the solid state diffusion of very fine, sub-micron size, colloidal graphite molybdenum disulphide powder. A coating of a mixture of these powder paints is applied, in preferred embodiment, to the surface of graphite inserts that becomes the casting face. The coating may be applied as a powder or as powders or, conveniently, as a slurry or suspension of such fine powders in deionized water and alcohol mixture.
As a different, but equivalent way of provide an oil-gas casting surface environment, castor oil, peanut oil or other lubricating oil may be delivered to either of the grooves suspended in a highly vaporizable liquid carrier such as alcohol, and the heat generated in the graphite ring during the casting operation is relied on to vaporize the carrier by the time it discharges at the inner peripheral face of the ring. The vapor of the carrier then becomes a part of the annulus about the metallic mass and may substitute entirely for the gaseous medium normally supplied to the grooves thus obviating any need for delivering gas to the same. Alternatively or additionally, the vapor of the carrier may be employed to modify the gaseous/vaporous character of the annulus, and/or to affect the top cooling of the metallic mass.
There are several possible embodiments of the invention, the preferred embodiment being depicted in the drawing and described hereinafter. These are, however, merely exemplary. In one embodiment, the graphite casting annulus insert components are so configured and constructed as to define a hook having a hook lip, said lip being snugly fitted in said annular groove for positioning and locking said insert components in said frame.
In another embodiment the graphite casting annulus insert components are configured and constructed to define a downwardly extending insertion lip which is snugly fitted in said annular groove for positioning and locking said insert components in said frame.
The support and cooling frame may define a second annular groove adjacent said annular face, and the graphite casting annulus insert components be configured and constructed to define a downwardly extending insertion lip, said downwardly extending insertion lip being snugly fitted into said second annular groove.
The invention includes a method of manufacturing a molten metal casting annulus that comprising an insert support and cooling frame configured and constructed to define an enclosed planar annular space and defining an annular face that faces the annular space and that is generally perpendicular to the plane of said annular space, the frame further defining an annular groove adjacent the annular face, and a large number of graphite casting annulus insert components supported entirely without clamping on said insert support and cooling frame, said insert components being fitted edge to edge around said annular face to define said annulus, the insert components having a lip snugly fitted in said annular groove for positioning and locking said insert components in said frame. The method comprises chilling the graphite casting annulus insert components before inserting the lip of the respective insert components into the annular groove in said frame and allowing said insert components to warm and thermally expand thereby locking the lip in position in said groove by thermally induced force between the insert component and the support frame.
The graphite casting annulus insert components may be configured and constructed to define a hook having a hook lip, in which case the method comprises chilling the hook lip, then inserting said chilled hook lip into said annular groove in said frame, and then allowing said lip to warm and thermally expand locking the lip in position in said groove by thermally induced force between the insert component and the support frame.
The frame define a second annular groove adjacent said annular face and the graphite casting annulus insert components may be configured and constructed to define, in addition to said hook lip, a downwardly extending insertion lip, and the method may comprise chilling said downwardly extending insertion lip, then inserting said chilled downwardly extending lip into said second annular groove in said frame, and then allowing said downwardly extending lip to warm and thermally expand locking said downwardly extending lip in position in said second groove by thermally induced force between the insert component and the support frame.
The invention contemplates a molten metal casting annulus comprising an insert support and cooling frame configured and constructed to define an enclosed planar annular space, said frame defining an annular face that faces said annular space and that is generally perpendicular to the plane of said annular space and a multiplicity of graphite casting annulus insert components supported entirely without clamping on said insert support and cooling frame. The insert components are fitted edge to edge around said casting annulus to define said annulus and secured thereto by thermally induced engaging force between said insert and said insert support and cooling frame and sealed to one another by said thermally induced engaging force.
The insert support and cooling frame is, in one preferred embodiment, configured and constructed to define at least one annular groove adjacent said annular face and the graphite casting annulus insert components are so configured and constructed as to define a hook having a hook lip, the lip being snugly fitted in said annular groove for positioning and locking said insert components in said frame.
The insert support and cooling frame may also be configured and constructed to define at least two annular grooves adjacent said annular face and wherein the graphite casting annulus insert components are so configured and constructed as to define an insert lip and to define a hook having a lip, said hook lip and said insert lips being snugly fitted in said annular grooves for positioning and locking said insert components in said frame. A special quality of graphite inserts to be used in the present invention is that the graphite material should allow solid diffusion of fine (submicron size) colloidal graphite powder mixed with fine (submicron size) molybdenum disulphide powder. A coating of these powder paints is applied, in preferred embodiments, on top of the inner surface wall, 40, of the graphite inserts. Additionally, the graphite inserts have the interconnected porosity to allow diffusion of lubricating oil in liquid or vapor form.
The invention is embodied, in one form, in a molten metal continuous casting apparatus comprising: a multiplicity of graphite casting annulus insert components, an annular insert support and cooling frame defining an insert supporting surface, and a annular closure plate, said insert support and cooling frame and said closure plate being configured and constructed to define, when secured together, an annular cooling fluid chamber. The insert support and cooling frame are configured and constructed to position said insert supporting surface in close thermal communication through a thermally conductive wall with the cooling fluid chamber and means are provided for securing the insert support and cooling frame and closure plate together to form said cooling fluid chamber. The multiplicity of graphite casting annulus insert components are secured in position on and receiving cooling from the insert support and cooling frame to define a planar annulus configured and constructed to serve as a surface against which molten metal can be cast for forming an ingot. The multiplicity of graphite casting annulus insert components are, in one of the more preferred embodiments, secured by thermally induced force to the annular insert support and cooling frame. The insert support and cooling frame may be configured and constructed to define an enclosed planar annular space, said frame defining an annular face that faces said annular space and that is generally perpendicular to the plane of said annular space, said frame further defined an annular groove adjacent said annular face. The graphite casting annulus insert components are supported entirely without clamping on said insert support and cooling frame, being fitted edge to edge around said casting annulus to define said annulus. The insert components may preferably comprise a lip snugly fitted in said annular groove for positioning and locking said insert components in said frame. Alternatively, or in addition, the graphite casting annulus insert components may be configured and constructed as to define a hook having a lip, said lip being snugly fitted in said annular groove for positioning and locking said insert components in said frame and/or a downwardly extending insertion lip likewise fitted in an annular groove for positioning and locking said insert components in said frame.